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Physicists Solve Low-Temperature Magnetic Mystery

From left, Jason Hancock, assistant professor of physics, and fellow researchers Diego Casa and Jung-ho Kim, with one of the instruments used in the experiment. (Argonne National Laboratory Photo)

Researchers have made an experimental breakthrough in explaining a rare property of an exotic magnetic material, potentially opening a path to a host of new technologies. From information storage to magnetic refrigeration, many of tomorrow’s most promising innovations rely on sophisticated magnetic materials, and this discovery opens the door to harnessing the physics that governs those materials.

The work, led by University of Connecticut professor Jason Hancock, and Ignace Jarrige of the Brookhaven National Laboratory, marks a major advance in the search for practical materials that will enable several types of next-generation technology. A paper describing the team’s results is published this week in the journal Physical Review Letters.

The work is related to the Kondo Effect, a physical phenomenon that explains how magnetic impurities affect the electrical resistance of materials. The researchers were looking at a material called ytterbium-indium-copper-four (usually written using its chemical formula: YbInCu4).

YbInCu4 has long been known to undergo a unique transition as a result of changing temperature. Below a certain temperature, the material’s magnetism disappears, while above that temperature, it is strongly magnetic. This transition, which has puzzled physicists for decades, has recently revealed its secret. According to Hancock, the new analysis shows that the material has a gap in its electronic spectrum, similar to the gap found in modern semiconductors.

The sample of YbInCu4 used in the experiment. (Brookhaven National Laboratory Photo)

Electronic energy gaps define how electrons move (or don’t move) within the material, and are the critical component in understanding the electrical and magnetic properties of materials. “Our discovery goes to show that tailored semiconductor gaps can be used as a convenient knob to finely control the Kondo Effect and hence magnetism in technological materials,” said Jarrige.

To uncover the energy gap, the team used a process called Resonant Inelastic X-Ray Scattering (RIXS), a new experimental technique that is made possible by an intense X-ray beam produced at a synchrotron operated by the Department of Energy and located at Argonne National Laboratory outside Chicago. By placing materials in the focused X-ray beam and sensitively measuring and analyzing how the X-rays are scattered, the team was able to uncover elusive properties such as the energy gap and connect them to the enigmatic magnetic behavior.

The new physics identified through this work suggest a road map for the development of materials with strong “magnetocaloric” properties, the tendency of a material to change temperature in the presence of a magnetic field.

A diagram of the RIXS experiment. (Image by Ignace Jarrige)

“The Kondo Effect in YbInCu4 turns on at a very low temperature of 42 Kelvin (-384F),” said Hancock, “but we now understand why it happens, which suggests that it could happen in other materials near room temperature.” If that material is discovered, he adds, it could revolutionize cooling technology.

Household use of air conditioners in the U.S. accounts for more than $11 billion in energy costs and releases 100 million tons of carbon dioxide annually. Use of the magnetocaloric effect for magnetic refrigeration as an alternative to the mechanical fans and pumps in widespread use today could significantly reduce those numbers.

In addition to its potential applications to technology, the work has advanced the state of the art in research. “The RIXS technique we have developed can be applied in other areas of basic energy science,” said Hancock, noting that the development is very timely, and that it may be useful in the search for “topological Kondo insulators,” materials that have been predicted in theory, but have yet to be discovered.

Join us for a talk by Gina Barreca,2018 UCONN BOARD OF TRUSTEESDISTINGUISHED PROFESSOR OF ENGLISH

All great works of fiction, poetry and dramaâas well as texts forming mythologies, religions, national epics to heroic sagasâhave loneliness at the heart of their narrative. From Persephone to Peter Pan, from âFrankensteinâ to âFrozen,â the stories we pass along are saturated with unwilling isolation.âOnly around half of Americans say they have meaningful, daily face-to-face social interactions,â according to a 2017 study. A former U.S. Surgeon General argues that âWe live in the most technologically connected age in the history of civilization, yet rates of loneliness have doubled since the 1980s.â We need more than social media. We need social contact. We need community. How can we break through the loneliness barrier? Being alone when in need of companionship is more than sad; itâs an epidemic.Chronic loneliness is as bad for your health as smoking 15 cigarettes per day. We need to change our national story and, often, our personal ones as well.Even the concept of the âlone wolfâ is a myth. Wolves hunt in packs.

Reception to follow.

For more information about this event, or if you are an individual who requires special accommodation to participate, please contact the CLAS Deanâs Office at (860) 486-2713.

A liberal arts and sciences degree prepares students with the tools they need to excel across a wide range of careers. Given the number of options available to you, it can be overwhelming to narrow down career choices. Attending CLAS Career Night will provide you exposure to career opportunities for CLAS students.

This semesterâs focus will be on research-based careers. During this event you will engage with CLAS alumni, learn about various occupations, and gain insight about how to best prepare for your future career.

The McNair Scholars Program and the Office of Undergraduate Research invite you to join us for a brown bag research seminar.

Birds, Bacteria, and Bioinformatics: Why Evolutionary Biology is the Best

Sarah Hird, Ph.D., Assistant Professor, Molecular and Cell Biology

This series is open to all undergraduate and graduate students, and is designed especially for students conducting (or interested in conducting) STEM research. These seminars are opportunities to learn about research being pursued around campus, to talk with faculty about their path into research, and to ask questions about getting involved in research.

About CLAS

The College of Liberal Arts and Sciences is the academic core of learning and research at UConn. We are committed to the full spectrum of academics across the sciences, social sciences, and humanities. We give students a liberal arts and sciences education that empowers them with broad knowledge, transferable skills, and an ability to think critically about important issues across a variety of disciplines.